Anatomy and physiology of the canine ear.

The canine ear consists of the pinna, external ear canal, middle ear and inner ear. The external ear is composed of auricular and annular cartilage. The auricular cartilage of the pinna becomes funnel shaped at the opening of the external ear canal. The vertical ear canal runs for about 1 inch, then forms the horizontal ear canal, which is composed of auricular and annular cartilage. The middle ear consists of an air-filled tympanic cavity, three auditory ossicles, and tympanic membrane. The tympanic membrane is a semitransparent membrane divided into the pars flaccida and pars tensa. The tympanic cavity consists of a small epitympanic recess, a large ventral bulla and the tympanic bulla proper. On the medial wall of the tympanic cavity is the promontory, which houses the cochlea. The cochlear (round) window is located in the caudolateral portion of the promontory, covered by a thin membrane. The vestibular (oval) window is located on the dorsolateral surface of the promontory, covered by a thin diaphragm over which the footplate of the stapes is attached. The auditory tube is a short canal that extends from the nasopharynx to the rostral portion of the tympanic cavity proper. The auditory ossicles are the bones that transmit and amplify air vibrations from the tympanic membrane to the inner ear. The inner ear is housed in a bony labyrinth in the petrous portion of the temporal bone. The bony labyrinth contains the membranous labyrinth with its sensory organs responsible for hearing and balance.